Rubberlike interpolymers of butadiene and methyl methacrylate and process for making same



Patented Giet. l5, 1940 UNlTED STATES t RUBBERLIKE INTERPOLYMES F BUTA-DIENE AND RIETHYL METHACRYLATE AND PROCESS FOR MAKING SAME Howard W.Starkweather, New Castle County, and

Arnold M. Collins, Wilmin to E. I. du Pont de Nemours & Company,Wilmmgto gton, Del., assignors n, Del., a. corporation of Delaware NoDrawing. Application March 9, 1939,V

Serial No: 260,758

11 Claims. (Cl. 26o-.84)

This invention relates-to the preparation of rubberlike products. Moreparticularly, it relates to the preparation of rubberlike products bythe polymerization of mixtures of -unsaturated compounds.

vIt has been disclosed in British Patent No. 360,- 82,2 that butadieneand certain acrylic acid esters, when dispersed in a suitableemulsifying solution, may be polymerized by heat to form prod- |0 uctsresembling natural rubber in many of their properties. Since, however,the polymerization is slow and great dimeulty is experiencedin obtainingeven passablelylelds of the rubberlike products, and since articles madefrom these poly- 5 mers are decient in certain important physicalproperties such as tensile strength and abrasion resistance, products ofthis type have received very little practical attention.. On the otherhand, British Patent No. 401,653 describes poly- 3 merization ofmethylmethacrylate in the presence of a wide4 variety ofotherpolymerizable materials and while it mentions, among these,butadiene and states further that the polymerizationscan be conducted ina waterygdispersion, it does not anywhere suggest the production ofrubberlike materials'and it is quite obvious from thedesc'ription of thematerials that the iatent is intended to cover that the patentees nevereven contemplated-the producten of rubrlike materials.`

, It is an object ci this invention to prepare new polymerizationproducts. `A more speciic object of the invention is to preparerubberlike materials from butadiene and polymerizable .estersofunsaturated acids. A further object is to prepare rubberlikematerials. having improved physical properties by polymerization ofmixtures of butadieneand polymerizable esters oi 'unsaturated acids. Astill further object is to develop.

0 a more rapidand emcient method for making such rubberlik'e products.'Other'objects will ap-H ed to limit the scope of the invention. The termpart's" whenever hereinafter used signiiles parts by Weight.

Example 1 Forty parts of butadiene (92% pure), 20 parts 5 of methylmethacrylate, and 76 parts of an. aqueous solution containing 2.3 partsof oleoamldoethyl dimethylamine hydrochloride,

and 0.24 part of acetic acid were introduced into a4 glass tube of sucha size that a vapor space of one third remained. The tube was thensealed and rotated about an axis perpendicular to its length in a bathat c. The butadiene and l5 methyl methacrylate dispersed readily in thesolution of the substituted ammonium salt. After 160 hours, the tube wasopened andthe thick dispersian of polymer was thinned with water and.coagulated by adding sodium chloride and ethyl alcohol. The coagulum waswashed with warm water and then .milled and dried on a rubber mill (withthe addition 0120.22 part of phenyl beta naphthylaminel' to form asmooth sheet. The 25 yield was of the total quantity of butadiene andmethyl methacrylate used.

Into parts of this product were incorporated by milling:

. Parts carbon black (comme black) 59 3. Zinc mzirin 5 steam 'fu-1d 2Sulfur- 2 Mercaptobenzothiazol 1.25

and the resulting compound was cured for 30 t minutes at 141 C. Theprodu't was very strong and elastic, having a tensile strength d! 3125lbs.' per sq. in. and an elongation at break of 400%.

' Example 2 sixty-nine grams of butadiene and 31 parts of methylmethacrylate were emulsiiled in 125 parts of an aqueous solutioncontaining parts of the dimethyl sulfate addition product-ot cetyl '45dimethylaminobenzoate',

and 0.4 part of acetic acid and heated for hrs. at 60 C. in` a steelautoclave hal! full. The 50 resulting polymer dispersion'was coagulstedby making it alkaline and maintaining it at 60 C. The coagulum waswashed. dried, and treated with phenyl betanaphthylamine as in Example,1, giving an 87% yield of a polymer which, when 55 compounded as inExample 1 (except that 10 parts of zinc oxide and 1 part of theaccelerator were usedland cured for 60 minutes at 141 C. gave a verystrong and elastic product which had a tensile strength of 3500 lbs. persq. in. and an elongation at break oi 265%.

` The ratio of butadiene to methyl methacrylate has 'an importantinfluence upon the properties of the polymerization product. In general,as

the proportion of methacrylate is increased, the

strength of the resulting product increases.4 Thus, with less than aboutby weight `of made 'with about 40% of methyl methacryiate.

As emulsifying agents any substances may be used which when dissolved inwater are capable of 'giving a permanent mixture of vbutadiene andmethyl methacrylate, although, since slightly acid dispersions are oftenused, the most suitable emulsitying .agents 'are those which give stableacid dispersions 4and which do not promote the hydrolysis of the esterto' an undesirable extent. It has beeniound that substituted ammonium orsulionium salts containing long chain (12 or more carbon atoms)hydrocarbon groups are particularly suitable.

.Examples oi' such agents in addition to' those given in Examples 1 and2 are: Cotyl trlmethyl ammonilnn bromide v It will be seen that allthese agents contain: pentavalen nitrogen atoms one valence of which isattached to a negative, ionizable, salt-forming radical. This may bebromide, chloride, acetate (CHsCOO-l methyl sulfate toluene sulfonate(C'zH1SOa-) or the carboxyl group. oi. a betaine. I'he long hydrocarbonchain may be attached directly to the form `"partof a more complicagroup. An example ofV a suitable sulfoniunr 'compound is c etyl dimethylsulfonium methyl sulfate. Another "type of agent which also gives goodree sults, particularly atpl9, is isopropyl mphthalene sodiumsuiion'ate.

A 2% or.3% solution-of the agents in water 4is usually suitableiorforming a good dispel'- sion but considerably stronger or weakersolutions, for example 0.2% to 10%,. may also be used. Thepolymerization is conveniently carricd out in a slightlyacid dispersionasin the .examples but it shouldbe understood that the,

dispersion may be either alkaline, or

In general, -the products most disperson in the water of therogen ormayA acid, provided that conditions are not such that the dispersion is.interfered with or coagulation induced or that the vmethyl methacrylateis hydrolyzed to an undesirable extent. Catalysts of polymerization maybe added, for example hydrogen peroxide, benzoyl peroxide, and ammoniumpersulfate and, in general,l the polymerization may be varied accordingto well known methods.

The ratio of the dispersed phase (butadiene and methyl methacrylate) towater may be widely varied. It is preferable that the amount, by weight,of water should be from about 100% to about 200% of the 'dispersedphase. Much more concentrated dispersions are so thick as to bedifllcult to agitate and may even suer in? More'dilute dispersionerequire uneconomically large reaction vessels.

The polymerizationm'ay be carried out at any version.

temperature from about 20 C. to about 100 C. or above. It has beenfound, however, that temperatures in the range between about 50 C. and

about .70 C.. are, in general,the most suitable. At lower temperaturesthe polymerization is usually tooslow while athigher temperatures moreelaborate equipment is required to withstand the high pressure andcertain properties of the preduct are adversely eii'ected.

The polymer dispersions may be coagulated' by any' of the known methodsapplicable to dispersions made with the particular dispersing agentemployed. Thus, some may' be coagulated as in Example 2 by making themalkaline and warming.4 Ethyl alcohol is .generally ap plicable tosubstituted ammonium salt disper sions. A more economical method is thatdisclosed in the copending application of Calcott and Youker, Serial No.181,602, flied December 24, 1'937, a preferred embodiment-of which (seeExample 2). consists of ilrst adding a saturated solution of sodiumchloride andthen adding a '1% solution of normal butyl alcohol inwater.l

In this way a rapid and complete coagulation is obtained with the use ofonly la small amount i of alcohol. Another application of this method isused in Example 1 above.- Coagulation may:

also be very advantageously brought about by the method disclosed in thecopending applica. tion of Calcott and Starkweather, Serial No..10'l,v

36o, med octobe 24, 1936. According toa preferred f orm o! thismethod,an internally cooled drum, part of which dips into the dispersion, isrotated in such a manner that a thin layer ofthe dispersion is frozenthereon and maintained at the low temperature out of contact l with theunfrozen dispersion for a time long enough fto cause completecoagulation. The froz en layer is then removed from the drum and warmed.A. continuous layer of coagulum results, which, because of its physicalform, is readily washed and dried.

The compounding of the products o! this 111-..

vention in general follows the principles lused for natural rubber.Thus, the presence or' an antioxidant o! the class eii'ective fornatural rubber is impopant, especially -since the synthetic materials,unlike the rubber, contain no natv uralantioxidant. The antioxidant isadvantageously added fn the form oi' a dispersion to the polymerdispersion before coagulation. Sulfur or :is eqmvalenafi usedwbringjabout vulcanization, .along with an organic vulcanization 4accelerator andq auxiliary agents such as zinc -oxide and stearic acid.In general. all of the nllins end reinfarcins usent! and pigments4 use'dfor rubber may be used here. Carbon black is particularly useful forreinforcing. Qtheragents known in the rubber art for softening,stiftening, reodorizing, or for producing or altering other specialproperties may also be added.

The products of rthe present invention may be used in the rubber art for`practically all'purposes for which' natural rubber is Moreover, whenIsuitably compounded and cured, they are much superior :to naturalrubber in several properties, notably resista-noe to abrasion and to theswelling action of oils and solvents. These products are thereforeparticularly suitable for making articles which are subjected in serviceto these influences. Examples oi' such applications are tire treads,gaskets, tubing, diaphragms and simil lar articles used in contact withoils and solvents; Both the products oi .the present invention and theprocess by winch they are made are greatly superior to those of theBritish Paten-t No.. 360,822 referred; to above. Examples 3 and 4 ofthis partent, involving the polymerization with butadiene of methylacrylate and butyl acrylate;.

respectively, have lbeen carefully repeated,` with the results thatyields of 18% and 50%,- respec- ,A

tively, were obtained in 113 hours at 60 C.,which is considerably longerthan the polymerization times given in the patent. When vcompounded andcured as in`Example 2 hereof.. theA tensile streng-tbs were 2 175 and1000 lbs. per sq. in. The

elngations were 190% and 160%, and the'abra- `sions were 0.120 and0.315, respectively. 'Ilhese .abra-sion iigures represent :the amountsof ma- ,agents and butadiene- .preparations of greater purity and madeby other methods, anni by polymerizing in the presence of celrbontetrachloride,

which es shown in the copendi-ng application of Habgood and Morgan,Serial No. 241,668, led Nov. 21, 1938, accelerates the polymerization ofthe butadiene-methyl methacrylate system. In no case did theseexperiments yield results approaching those obtained according tothepres- Vent invention. 'I'.he difference between the products of thepresent invention and those of Bultish Patent No.401,653 is perhaps evenmore striking in thatrthe products of the patent are'resinous in naturewhereas rthose preparedas disclosed herein are rubberllkel Y 'rhosuperiority or methyl motnoorylate over4 the acrylates for formingrubberlike prodl'tcts.V

with butadiene is entirely unexpected. In fact,

the statements in the literature indicute that methyl mthacrylate wouldbe much-inferior for this purpose. -Thus, Neher v(Ind. Ens.' Chem. '28,267 (1936)) states that; acrylates polymeri'ze much luster-v andtherefore more violently v'than 4the corresponding :oreillecryliltes.;and that' whereas polymethyl acrylate is a rather sott, elastic,rubberlike' substance,- polymethylmethacryhteisahardrrtoughmesswlnchcanbe 3 sawed, carved, or worked'on alathe with easef 'I'hese statements would certainly lead one away from.the use of methyl methacrylalte for the rapid production of rubberlikematerials.

'I'he above description and examples are in- '5 'tended to beillustrative only. Any modicaltion of or variation therefromwhichc'oniorms to the spirit of the inventionis intended to be includedabout 15% .to about 50% of the weight or the lt two polymerizable`materials is methyl meth--` 2. The process for making r-ubberlikematerials which comprises dispersing in water containing l a smallamount of emu-lsifying agent a mixturel 20 of butadiene andmethylmethac-rylate inwhich from about 15%, to about 50%' or the'welgnt'of the two polymer-mole materials .ls methyl methacrylate, andthen polymenizirlg :the mixture so dispersed.

3. The process of claim 2, i'urither characterized in that fromaboult.30% to about 50% of methyl methacrylafte.

the weight of the .two polymellzablo materials ls vf in that aboutv 40%of the weight-oi thewtwo polyf merizable materials is methylmethaorylate.

. 5. V'Ilie processor claim 2, further characterized in that the polymerm'icoagulated, washed, dried, compounded, and cured.

' 6. The process of claim 2, further' characterized r lu that fromobout.3o% yto about 50% of the weight -of the two polymerizablematerials is methyl lmethacrylate and in thatrthe pclymeris coagulated.washed, dried,- compounded, and 4o cu-red.

. '1. A polymer obtained by the 'process oi' claim 1.. l8. A polymerobtained -by dispersing in water in the presence of an emulsifying agenta mixture of butadiene and methyl methacrylate in which .from 'about'30% .to about 5,0% of the weight of the yrtwo vporlymerizable materialsisv methyl methacrylate and then polymerizing the mixture while sodispersed.'

' '9. 'A1 polymer obtained 'bydispersing in water.- 604 in the presenceof an emulsi-fying agent a mixo! butadieneand -methyl meth'wcrylate inwhich'irom about 30% ltoabout 50% o! the weight of vIthe twopolymerizable materials is methyl methacrylalte and then polymerizingthe mixture wlhile so dispersed, and -lthereaiter coagulating thepolymer, washing, drying, compounding, and curing it.

10. A polymer obtained by compounding and curing a polymer obtained -byfthe processor 60 -oloim l.

1l. A polymer obtalnedfoy .the process of' claim 2, furtherchal-aoterlzea ln that it ls-made'from a mixture of butadiene and methylmethacrylate in which about 40% oi' .the weight of the two .05

4. The process of claim 2, further characterized 30

